The present invention relates to lidded containers capable of withstanding an internal pressure. The invention is particularly useful for plastic lidded containers, and is therefore described below with respect to this application.
Containers closed by lids are commonly used in storing and shipping goods, particularly goods in the form of flowable materials, such as liquids, pellets, pastes, powders and the like. Where the container may be subjected to an internal pressure, it is necessary to make the container, and particularly the attachment of the lid to the container, sufficiently strong to withstand such internal pressures. This is particularly problematic with respect to containers made of plastic materials (as distinguished from metal or glass), since plastic generally is more deformable under pressure. Plastic containers are highly susceptible to deformation under pressure, particularly at the attachment of the lid to the container rim, which may result in leakage because of loosening of the lid. Therefore lidded containers, and particularly the area of attachment of the lid to the container, must be made of sufficient thickness to withstand such internal pressure. As a result, the lidded containers are relatively costly to produce because of the added material needed, are relatively costly to transport because of the increased weight, and are environmentally unfriendly because of the relatively large amount of plastic material to be disposed of.